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Raid-II: A High-Bandwidth Network File Server

Raid-II: A High-Bandwidth Network File Server. Ann L. Drapeau, Ken W. Shirriff, John H. Hartman, Ethan L. Miller, Srinivasan Seshan, Randy H. Katz, Ken Lutz, David A. Patterson, Edward K. Lee, Peter M. Chen, Garth A. Gibson. Introduction. Why do we need RAID-II?

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Raid-II: A High-Bandwidth Network File Server

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  1. Raid-II: A High-Bandwidth Network File Server Ann L. Drapeau, Ken W. Shirriff, John H. Hartman, Ethan L. Miller, Srinivasan Seshan, Randy H. Katz, Ken Lutz, David A. Patterson, Edward K. Lee, Peter M. Chen, Garth A. Gibson

  2. Introduction • Why do we need RAID-II? • Many new applications require larger amounts of data. • Computer Aided Design • Databases • Multi-media • Scientific Simulations • Raid-I is unable to provide the needed I/O bandwidth.

  3. The Need For Speed • RAID-I • Redundant Arrays of Inexpensive Disks • Performs well when processing small random I/O requests. • Inadequate for high-bandwidth I/O requests. • Coping data between kernel DMA buffers and buffers in user space saturate the memory system when I/O bandwidth reaches 2.3 mb/s. • Data must go through the CPU’s virtual addressed cache and cache flushes slow the performance. • Bandwidth restricted by the VME system bus (9 mb/s).

  4. Raid-II • RAID-II contains two data paths • High-bandwidth (HIPPI) • Handles large data transfers. • Low-bandwidth (Ethernet) • Handles metadata and small data transfers. • LFS – Log Structured File System

  5. High-Bandwidth Data Path • XBUS • Allows large data requests to bypass the server workstation. • Connects the disks directly to the high speed HIPPI network. • The HIPPI network is the high speed network with a transfer rate of 100MB/s. • It takes about 1.1 milliseconds to transfer a HIPPI packet. (Due to setup of HIPPI & XBUS control registers)

  6. Low-Bandwidth Data Path • Uses Ethernet capable of 10 Mb/s = 1.25 MB/s. • Used to transfer the metadata and small data requests. • It takes about 0.5 milliseconds to transfer a packet on Ethernet. (HIPPI takes 1.1 ms)

  7. RAID-II

  8. XBUS Controller Board

  9. Raid-II file system • LFS = Log Structured File System • Writes all file data and metadata to an append only log file. • This minimizes the number of small writes to the disk, by buffering the writes and then writing a single large sequential file to the disk. • Also provides fast crash recovery.

  10. Raid-II file system • Modified LFS • Must be able to separate requests among the high and low bandwidth data paths. • Manage the memories on the host workstation and the XBUS board. • Cache coherency

  11. Conclusions • RAID-II allows data to be transferred between disks and the HIPPI network without going through the low-bandwidth memory by using the XBUS controller cards. • RAID-II uses LFS to buffers small writes into large requests to avoid wasting disk bandwidth.

  12. ¿Questions? • What was the purpose of designing the XBUS controller board? • Describe the two network connections used and their purposes. • What additional ideas could be applied to RAID-II to improve performance?

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